Glioblastoma multiforme (GBM) is a common type of primary brain tumor in humans and is a very aggressive and devastating cancer, with a median survival of approximately one year. (Eramo et al., Chemotherapy resistance of glioblastoma stem cells, Cell Death and Differentiation (2006) 13, 1238-1241). Glioblastoma has the worst prognosis of any central nervous system malignancy. Therapy for GBM is difficult due to its biological location in the brain. Current treatments can involve chemotherapy, radiation, radiosurgery, corticosteroids, antiangiogenic therapy, and surgery. Despite the development of new surgical and radiation techniques and the use of multiple antineoplastic drugs, a cure for malignant gliomas does not exist. (Eramo et al., Chemotherapy resistance of glioblastoma stem cells, Cell Death and Differentiation (2006) 13, 1238-1241). Glioblastoma cells are resistant to cytotoxic agents, and the high incidence of recurrence in a very short period of time in glioblastoma patients suggests that tumorigenic cells are capable of overtaking the treatments.